The majority of the world's population suffers from insufficient access to quality health care, partly attributed to the inaccessibility of vaccines in isolated rural areas as well as inconsistent temperature control during the transportation of these vaccines. An exemplary target application is the treatment of Human papillomavirus (HPV), which is a sexually transmitted infection that is currently responsible for 50-60% percent of cervical cancer outbreaks in Ugandan women. This infection causes 3,500 women to be diagnosed with cervical cancer annually in Uganda and 2,400 women die as a result. If preliminary measures are taken, adolescent women from 9-13 years old treated with the HPV vaccine have a 95% chance of preventing the infection. A majority of these adolescent women, as with 86.7% of the Ugandan population, live in rural areas. In these regions, there are limited resources such as a reliable electricity source, so the off-grid transportation of medicines is crucial for maintaining a constant supply chain for vaccines, also known as the cold chain. This concept known as “last-mile distribution” has become a major focus for humanitarian and relief groups, since there is little success in maintaining the efficacy of vaccines during the last stage of transportation.
There are many methods for maintain insulin and other medicines within their required temperature ranges. One very common method utilizes re-freezable ice/gel packs to cool down the designed chamber. The cooling lifetime for these designs is dependent on the length of time that the packs stay frozen and how well the chamber is insulated. While cost is typically low, reliability of the system is an issue. Most other portable medicine cooling devices utilize the temperature difference generated by thermoelectric devices to maintain within a temperature range. However, existing designs cannot reach a temperature difference of 30 K. This makes their effectiveness greatly dependent on outside temperature. An early design used a battery and cooler section joined by thermoelectric material. The electric supply to the thermoelectric device is controlled by a temperature dependent relay. Further advances in controlling temperature utilizes a redundant battery source and the microcontroller power supply strategy take into account the desired temperature range, substance being cooled, and initial battery capacity to maximize battery life. The addition of a low thermal conductivity material, Aerogel, helps to prevent heat leakage into the cooled chamber. With such a high insulation, good heat dissipation is important and has been achieved by designs in various ways. A Thermoelectric Medicine Cooling Bag utilizes a cutaway section for a heat sink to protrude from their design to dissipate heat. One device uses a heat sink to remove heat from the cooled chamber, but in conjunction with a fan to increase the heat sink's heat transfer coefficient. A method for removing heat from the thermoelectric module's hot side is through melting salt has been shown.
What is needed is a mobile vaccine cooler to safely transport and distribute vaccines at their proper storage temperature in developing nations, using thermoelectric modules as a solid-state cooling device.